Reverse-turns are structures which reverse the direction of a polypeptide chain. When they connect antiparallel .beta.-strands, the reverse turns are also known as .beta.-turns, .beta.-bends, and hairpin turns. Reverse-turns can be described as tetrapeptide sequences. However, the most critical parameters are the the torsion angles of the second and third residues. The first and fourth residues may or may not form hydrogen bonds. As a result of geometric requirements, Asn, Ser, Asp, and particularly Gly or Pro are often present.